Most high-definition television receivers (HDTVs) display picture information in a 16:9 aspect ratio. Earlier video productions utilize Legacy Video Programming (LVP) in which the picture has a 4:3 aspect ratio. It is possible for broadcasters to fit legacy video inside a 16:9 window by transmitting the legacy video along with black bars on either edge of the screen. From a receiver standpoint, it is possible to stretch the legacy video horizontally to fill up the full width of the screen. However, the receiver must first find the edges of the black bars.
A black bar detection algorithm was implemented in earlier Texas Instruments video receivers decoding high-definition television (HDTV) signals. In these systems the reverse process works equally well. In the reverse process a 16:9 aspect ratio video raster is broadcast in a 4:3 aspect ratio picture with black bars at the top and bottom.
Digital Terrestrial TV has no adjacent channel interference problems, so they may be sited in adjacent frequency bands. The frequency range for US Digital TV (ATSC) is the same range as Analog TV. The 6 MHz spectrum allocated for digital TV stations were sited in the unused sites within the broadcast TV blocks in the Analog TV spectrum. It was a requirement for digital TV modulation to not interfere with Analog TV. The US Digital TV Standard is called Advanced Television Systems Committee (ATSC). Since the frequency range for US Analog TV and ATSC Digital TV is the same, the same tuner can be used for both.
FIG. 1 illustrates usage of the display processor in set-top box applications. The antenna 101 captures a portion of the broadcast RF spectrum. RF tuner 102 captures a particular channel from antenna source 101. Cable 103 receives input from a cable television source. RF tuner 104 captures a particular channel from cable 103. For satellite reception, a parabolic dish directs microwave frequency spectrum to a focal point where a Low Noise Block (LNB) 105 resides. The LNB outputs baseband intermediate frequency (IF), which is fed through coaxial cable to a set-top box.
The RF Tuner 102 isolates a single 6 MHz band and usually outputs Intermediate Frequency Baseband. Since the frequency ranges for US terrestrial Analog TV and ATSC digital TV are the same, the same tuner can support both. The cable frequencies are in a similar range to terrestrial broadcast frequencies. Usually the same tuner design can be used for cable as for terrestrial broadcast. Multiplexer 106 selects one of these three intermediate frequency (IF) signal as output 107.
The demodulator 108 extracts a digital bitstream from the IF modulated signal 107 and passes the demodulated information 109 to the video processor 110. The digital bitstream 109 carries Forward Error Correction data, which may be used to correct or at the very least detect errors in the transmission. The error corrected Transport Packets contain time multiplexed compressed video, compressed audio, and system information.
The majority of TV display devices 112 and 113 utilize a 16:9 LCD or Plasma panel. The input is digital red-green-blue (RGB), which is saved into a frame buffer memory inside the LCD panel displays 112 and 113.
The HDMI unit 111 provides the standard interface for connecting DVD players or set-top boxes to HDTVs. HDMI carries uncompressed digital video. Audio is inserted in the blanking periods of the uncompressed video and can be uncompressed pulse code modulation (PCM) or compressed in several different formats. The transmitted signal is a digital bitstream with error correction. ATSC uses a modulation scheme called Vestigial Sideband Modulation (VSB). US cable systems typically use Quadrature Amplitude Modulation (QAM). US satellite systems use Quadrature Phase Shift Keying (QPSK).
FIG. 2 illustrates a prior art video receiver system implemented as a system on chip (SoC) 200 that integrates the main functions of a digital television (DTV) receiver. SoC 200 receives four inputs signals. Digitized PCM audio input drives inter-IC sound (I2S) input 211. The output of I2S input 211 feeds memory interface (MI) 210. MI 210 controls data transport between inputs and outputs. Digitized video input drives video input buffer (NV) 212 which in turn drives MI 210. Analog video input drives NTSC/PAL/SECAM decode unit 213. NTSC/PAL/SECAM decode unit 213 converts the analog input in one of three analog video standards National Television Standards Committee (NTSC), Phase Alternating Line (PAL) or Sequential Couleur Avec Memoire (SECAM) into digitized video for input to NV 212. Transport packet parser (TPP) 214 receives an input transport bitstream. TPP 214 typically includes support for OpenCable™ point of deployment (POD) for interface to digital cable. This data is further processed by packetized elementary stream (PES) parser 215 with its output going to MI 210.
SoC 200 includes several intermediate processing units that transfer data to and from MI 210. Audio processor 221 supports multiple audio formats decoding and processing. MP@HL MPEG-2 Video Decoder 222 fully decodes all advanced television standards committee (ATSC) digital television (DTV) video formats. Central processing unit (CPU) 223 controls the memory mapped internal devices and runs the application software. On-chip peripherals 224 are integrated into current display processors to further reduce system cost. On-chip peripherals 224 may include one or more universal asynchronous receiver/transmitters, programmable infrared (IR) input and output ports, a SmartCard interface, an extension bus to connect peripherals such as display and control panels and additional I2C interfaces. On-chip peripherals 224 may be bidirectionally coupled to MI 210 (not shown).
SoC 200 includes a mixed memory interface. This included direct memory access (DMA) unit 225 connected to MI 210 and to external bus interface 226. External bus interface 226 handles access to random access memory (RAM) 241, read only memory (ROM) 242 and Flash memory 243. Double data rate memory interface (DDRI) 244 interfaces with MI 210 and exchanges data with synchronous dynamic random access memory (SDRAM) 245.
SoC 200 includes a number of outputs. Audio output controller (AOC) 231 receives data from MI 210. AOC 231 outputs PCM audio and supplies PCM audio to NTSC encoder 236. Display Processor 232 includes the ability to convert any ATSC DTV format to any other format, including non-standard display resolutions support for panel based DTVs. On-screen display (OSD) controller 233 also includes a 2D graphics accelerator and supports applications with laid on text such as a sophisticated Graphical User Interface (GUI). High definition (HD) encoder 234 receives video data from MI 210 via OSD controller 233 and generates a digital signal for a corresponding HD display. This digital signal may be directly output from SoC 200 via digital video output. This digital signal also supplies video digital to analog converters (DAC) 235. Video DACs 235 generate analog signals to drive displays requiring such signals. These analog signals are generally output as color component signals or as a composite video signal. The output selected corresponds to the particular attached display device. NTSC encoder 236 receives data from MI 210, from AOC 231 and from display processor 232. NTSC encoder 236 generates a NTSC standard signal supplied to video DACs 235 for output as color component signals or as a composite video signal.